Conductive particles are widely used for anisotropic conductive materials such as anisotropic conductive paste, anisotropic conductive ink, an anisotropic conductive pressure sensitive adhesive/an anisotropic conductive adhesive, an anisotropic conductive film and an anisotropic conductive sheet by mixing them with a binder resin or a pressure sensitive adhesive/an adhesive and kneading.
These anisotropic conductive materials are used in the form that they are interposed between opposed boards or between opposed electrode terminals of electronic devices such as a liquid crystal display, a personal computer and a mobile telephone in order to electrically connect a board to another board or to electrically connect a small part such as a semiconductor device to a board.
As the conductive particles used for the above anisotropic conductive materials, there have been previously employed a conductive particle in which a metal-plated layer is formed as a conductive film on the surface of a nonconductive particle such as a resin particle having a uniform particle diameter and moderate strength. However, in recent years, as electronic devices have been sharply progressing and developing, further reduction of the connection resistance of the conductive particles used for the anisotropic conductive materials have been required.
In Japanese Unexamined Patent Publication No. 4-36902 and Japanese Unexamined Patent Publication No. 2000-243132, there are reported a conductive particle having projections on their surface as a conductive particle for reducing the connection resistance of the above conductive particle.
In Japanese Unexamined Patent Publication No. 4-36902, there is described a conductive particle prepared by metal-plating the surface of a nonconductive particle, which is provided with projections on its surface. However, this is a particle with projections formed from a combined particle of a mother particle and child particles, and plastic or glasses such as silicate glass were used for a projection portion of this particle. Accordingly, materials composing the projection were nonconductive, and it was difficult to reduce the connection resistance and improve the conductivity.
In Japanese Unexamined Patent Publication No. 2000-243132, there is described a method of producing a conductive electroless plated powder by simultaneously forming minute nickel projections and a nickel coat on a nonconductive particle through the use of the self-decomposition of a nickel plating solution in an electroless nickel plating method. However, in this production method, since it was extremely difficult to control the size, the shape and the amount of a minute nickel particle with which a projection was formed, it was extremely difficult to control the number, the size, and the shape of the projection to be obtained. And, since the minute particle was deposited and produced in the step of plating by using a nickel plating solution containing much phosphoric components, it had a disadvantage that conductivity was deteriorated due to the much content of phosphorus.